The present invention relates to a control system for an automatic transmission, and more particularly, to a control system for a vehicle, which is provided with an idle stop controller for stopping engine idle at a standstill of the running vehicle.
In recent years, idle stop vehicles are already operational wherein when the running vehicle comes into a standstill, and predetermined stop conditions are formed, an engine is automatically stopped to achieve fuel savings, a reduction in exhaust emission or noises and the like. With such vehicle, when the engine is stopped, a main pump driven by the engine is stopped, so that oil supplied to a forward clutch of an automatic transmission is also drawn from a hydraulic passage, lowering the hydraulic pressure.
As a result, when the engine is restarted, the forward clutch to be engaged at forward running also releases from its engagement state. Thus, if the forward clutch is not engaged quickly at engine restart, an accelerator pedal is depressed in the neutral state as it were, which may produce an engagement shock by engagement of the forward clutch with the engine at full throttle.
Therefore, the technique described, for example, in JP-A 2000-46166 is known as means for solving this.
This technique uses two pumps wherein the main pump is operated to supply fluid, and the assist pump driven by an electric motor is operated solely at stop of the main pump such as at engine stop to compensate for flow shortage, allowing secured supply of working fluid to the automatic transmission while keeping power consumption of a battery at the minimum.
However, in the above-mentioned prior art, the assist pump driven by the electric motor is always driven at engine stop, leading to significant power consumption. Particularly, at traffic congestion or the like, there arose a problem that a great load is applied not only to the battery, but also to the motor itself for driving the assist pump.
Moreover, since the assist pump is driven by the electric motor, the pump and the electric motor should be mounted on the automatic transmission, raising a problem of deteriorating the vehicle mountability.
The present invention aims to provide a control system for an automatic transmission having as a hydraulic-pressure supply source a main pump driven by an engine, wherein at idle stop control, the main pump is stopped to supply the hydraulic pressure required for running at restart, allowing smooth running.
The present invention is made in view of the problem in the prior art as mentioned above. The invention as described in claim 1 provides a control system for an automatic transmission in a vehicle comprising: an engine including a starter motor for start and idle-stop control means for outputting signals for idle operation and stop for the engine to an engine control unit in accordance with preset idle stop conditions and on the basis of a vehicle speed signal sensed by a vehicle speed sensor, a steering angle signal sensed by a steering angle sensor, a signal out of brake operation detecting means for detecting brake operation and the like; and an automatic transmission for performing speed change control using as a hydraulic-pressure supply source a main pump driven by said engine, characterized by arranging a bypass hydraulic passage for ensuring communication between said main pump and a point immediately before an engagement-pressure supply port of a forward engagement element in the automatic transmission, a switching valve on said bypass hydraulic passage to allow switching between a communication state and a non-communication state, and switching-valve control means for switching said switching valve between the communication state and the non-communication state.
The control system for an automatic transmission as described in claim 1 includes no electric assist pump and the like in the prior art, so that when engine idle is stopped by idle-stop control means, the electric assist pump is not continuously operated during idle stop as well.
Therefore, idle stop control can be performed without applying a load to the battery and the electric motor and at low cost.
Moreover, the bypass hydraulic passage is arranged to ensure communication between the main pump with a point immediately before the engagement element, and the switching valve is arranged on the bypass hydraulic passage to switch between the communicating state and the non-communicating state. Therefore, by directly supplying oil to the hydraulic passages having oil discharged therefrom without waiting switching of the hydraulic passages by the shift valves, sufficient engagement pressure can quickly be supplied to the engagement element.
Further, the invention as described in claim 2 provides a control system for an automatic transmission in a vehicle comprising: an engine including a starter motor for start and idle-stop control means for outputting signals for idle operation and stop for the engine to an engine control unit in accordance with preset idle stop conditions and on the basis of a vehicle speed signal sensed by a vehicle speed sensor, a steering angle signal sensed by a steering angle sensor, a signal out of brake operation detecting means for detecting brake operation and the like; and an automatic transmission for performing speed change control using as a hydraulic-pressure supply source a main pump driven by said engine, characterized by arranging a bypass hydraulic passage for ensuring communication between said main pump and a point immediately before an engagement-pressure supply port of a forward engagement element in the automatic transmission, and switching-valve control means for switching said switching valve to the communication state during a predetermined time period when said idle-stop control means output a release command for releasing an idle stop of the engine after said idle stop.
In the control system for an automatic transmission as described in claim 2, the bypass hydraulic passage is arranged to ensure communication between the main pump with a point immediately before the engagement element, and the switching valve is arranged on the bypass hydraulic passage to switch between the communicating state and the non-communicating state.
And the switching-valve control means are arranged for switching the switching valve to the communication state during a predetermined time period at engine restart. Specifically, in the conventional hydraulic circuit for an automatic transmission, as shown, for example, in FIG. 10, the shift valves are arranged to perform switching of the hydraulic passages for supplying to the engagement elements the hydraulic pressure generated by the oil pump. The shift valves are actuated to switch the hydraulic passages, allowing engagement of the engagement elements and the like. At first speed start, for example, the pilot pressures are supplied to the shift valves A, B, C to supply the engagement pressures to the low clutch L/C and the reduction brake RD/B.
However, switching of the hydraulic passages by the shift valves requires a certain hydraulic pressure, which is produced after charging oil in the hydraulic passages having oil discharged therefrom once, requiring certain time for charging oil.
As a result, unless switching of the hydraulic passages is performed by the shift valves, the hydraulic pressure is supplied to the reduction brake RD/B, the 2-4 brake 2-4/B, and the high clutch H/C as shown, for example, by the hatched portions in FIG. 10, falling in fourth speed.
Then, in the invention of the present application, the bypass hydraulic passage is arranged in the engagement elements for first speed engagement so as to supply oil to the hydraulic passages having oil discharged therefrom without waiting switching of the hydraulic passages by the shift valves. By directly supplying oil to the points immediately before the engagement elements during a predetermined time period, sufficient engagement pressure can quickly be supplied to the engagement elements.
Moreover, since the switching-valve control means include means for switching the switching valve to the communication state during a predetermined time period when the idle-stop control means output a release command for releasing an idle stop of the engine after the idle stop, sufficient engagement pressure can quickly be supplied to the engagement elements at completion of idle stop control. Further, since the switching valve is put in the non-communication state aster a lapse of the predetermined time period, control can be made only with a timer and the like, resulting in simplification of control and reduction in cost.
Still further, the invention as described in claim 3 provides the control system for an automatic transmission as described in claim 1 or 2, wherein said switching-valve control means include means for driving said starter motor by an output of a release command for releasing an idle stop of the engine when the engagement pressure of said forward engagement element is greater than a predetermined value, or after the idle stop by said idle-stop control means, and for switching said switching valve to the non-communication state when outputting a signal for stopping driving of said starter motor after completion of engine start.
In the control system for an automatic transmission as described in claim 3, by stopping driving of the starter motor by engine restart (i.e. in the state where the main pump is driven with engine complete explosion to secure sufficient hydraulic pressure), the switching valve is switched to the non-communication state so as to allow supply of only the required hydraulic pressure to the forward engagement element. Thus, during normal running, smooth running can be achieved without having an influence on speed change control of the automatic transmission and the like.
Furthermore, the invention as described in claim 4 provides the control system for an automatic transmission as described in claim 1 or 2, wherein it comprises an orifice on a hydraulic passage for supplying a hydraulic pressure to each engagement element formed in the automatic transmission and said switching valve, wherein a diameter of the orifice of said switching valve is se to be more than twice as large as that of the orifice on the hydraulic passage of said each engagement element.
In the control system for an automatic transmission as described in claim 4, the diameter of the orifice of the switching valve is more than twice as large as that of the orifice of each engagement element. Specifically, as shown in FIG. 6, the normal hydraulic circuit for an automatic transmission is provided with orifices d1, d2, d3, d4 to prevent the surge pressure immediately after engagement of each engagement element. At this time, the oil amount is proportional to the square of the orifice diameter.
In the state where the pilot pressures are not sufficiently supplied to the shift valves 41, 42, 43, oil is supplied to the reduction brake RD/B, the 2-4 brake 2-4/B, and the high clutch H/C to supply the oil amount proportional to the diameters d2, d3, d4 (d2 greater than d3 greater than d4) of the orifices located on this hydraulic passage. Moreover, when oil is supplied to the low clutch L/C through the bypass hydraulic passage, the diameter of the orifice of the switching valve is set to be more than twice as large as the largest one d2 of the orifice diameters d2, d3, d4, wherein assuming that the flow rate of oil supplied to the low clutch L/C is Q, and the pump discharge amount is Q1,                     Q        =                  xe2x80x83                ⁢                              4            ⁢                          d2              2                        ⁢                          Q1              /                              (                                                      4                    ⁢                                          d2                      2                                                        +                                      d2                    2                                    +                                      d3                    2                                    +                                      d4                    2                                                  )                                               greater than                       4            ⁢                          d2              2                        ⁢                          Q1              /                              (                                                      4                    ⁢                                          d2                      2                                                        +                                      d2                    2                                    +                                      d2                    2                                    +                                      d2                    2                                                  )                                                                            =                  xe2x80x83                ⁢                              4            ⁢                          Q1              /              7                                =                      0.57            ⁢                          xe2x80x83                        ⁢            Q1                              
It will be thus understood that about 60% of the discharge oil amount of the main pump can be supplied to the low clutch L/C. Therefore, sufficient oil amount can be supplied to the engagement elements required at engine restart, achieving smooth running.
In the invention as described in claim 4, the diameter of the orifice of the switching valve is set to be more than twice as large as the largest one d2. It is needless to say that the orifice diameter can be determined as appropriate by computing with the above-mentioned expression the orifice diameter which can secure the oil amount sufficient for the forward engagement elements in other hydraulic circuits, for example.
Further, the invention as described in claim 5 provides the control system for an automatic transmission as described in claim 1 or 2, wherein said idle-stop control means include means for prohibiting an idle stop when a select position selected by a driver is an R range or in a reverse state, and when a detected oil temperature fails to be within a predetermined range.
In the control system for an automatic transmission as described in claim 5, idle stop control is prohibited when the select position is at the R range.
Specifically, as shown in the engagement table in FIG. 3, at the first speed, the hydraulic pressure should be supplied to the low clutch L/C and the reduction brake RD/B. Even in the state where the shift valves do not switch the hydraulic passages, the hydraulic pressure is supplied to the reduction brake RD/B, and thus the hydraulic pressure needs to be supplied to the other part or the low clutch L/C only through the bypass hydraulic passage.
However, at the R range, the hydraulic pressure should also be supplied to the reverse clutch R/C and the low and reverse brake LandR/B, and thus it is difficult to supply the oil amount required for engagement before engine start. Then, at the R range, idle stop control is prohibited, allowing achievement of idle stop control without having complicated constitution and thus at low cost.
Moreover, idle stop control is prohibited when the oil temperature fails to be within a predetermined range. Specifically, if the oil temperature is too low, the viscosity resistance of oil becomes too high, resulting in impossible supply of sufficient oil amount before engine start. On the other hand, if the oil temperature is too high, the oil viscosity becomes too low, causing a decrease in volumetric efficiency of the main pump and an increase in leakage amount at the valve parts, resulting in impossible supply of sufficient oil amount in the same way.
Therefore, with idle stop control being prohibited when the oil temperature fails to be within a predetermined range, the engine is not stopped except when oil can surely be supplied at engine restart, allowing achievement of smooth idle stop control without having complicated constitution and thus at low cost.
Still further, the invention as described in claim 6 provides the control system for an automatic transmission as described in claims 1 to 3, wherein said forward engagement element is provided with engagement-pressure detecting means for detecting an engagement pressure and engagement-pressure comparing/determining means for comparing the detected engagement pressure and a predetermined engagement pressure set in advance for allowing securing of an engagement pressure, wherein said switching-valve control means include means for switching the switching valve to the non-communication state when said engagement-pressure comparing/determining means determine that the detected engagement pressure is greater than said predetermined engagement pressure.
In the control system for an automatic transmission as described in claim 6, the engagement-pressure detecting means are provided to detect an engagement pressure of the forward engagement element, and the engagement-pressure comparing/determining means compare the detected engagement pressure and a predetermined engagement pressure set in advance for allowing securing of an engagement pressure.
And if it is determined that the detected engagement pressure is greater than the predetermined engagement pressure, the switching-valve control means switch the switching valve to the non-communication state. Specifically, if the required engagement pressure is secured, it is not necessary to supply oil further from the bypass hydraulic passage.
Therefore, detection of the engagement pressure allows the bypass hydraulic passage to be put in the non-communication state with optimum timing, resulting in efficient use of the discharge oil amount of the main pump.
Furthermore, the invention as described in claim 7 provides the control system for an automatic transmission as described in claim 1 or 2, wherein said switching valve includes a solenoid valve comprising a return spring and an electromagnetic solenoid for generating an electromagnetic force opposite to the return spring, and said engagement-pressure detecting means and said engagement-pressure comparing/determining means include a feedback-pressure circuit for supplying from the downstream side of said solenoid valve a hydraulic-pressure force opposite to an electromagnetic force of said electromagnetic solenoid.
Therefore, in the control system for an automatic transmission as described in claim 7, the switching valve includes a solenoid valve comprising a return spring and an electromagnetic solenoid for generating an electromagnetic force opposite to the return spring, and the engagement-pressure detecting means and the engagement-pressure comparing/determining means include a feedback-pressure circuit for supplying from the downstream side of the solenoid valve a hydraulic-pressure force opposite to an electromagnetic force of the electromagnetic solenoid.
Thus, even if the switching-valve control means output a signal for maintaining the communication state of the bypass circuit during a predetermined time period, for example, if the hydraulic pressure supplied from the feedback-pressure circuit reaches a predetermined oil pressure, the bypass circuit can be put in the non-communication state without waiting a signal out of the switching-valve control means, achieving switching control of the switching valve with optimum timing.
Further, the invention as described in claim 8 provides a control system for an automatic transmission in a vehicle comprising: an engine including a starter motor for start and idle-stop control means for outputting signals for idle operation and stop for the engine to an engine control unit in accordance with preset idle stop conditions and on the basis of a vehicle speed signal sensed by a vehicle speed sensor, a steering angle signal sensed by a steering angle sensor, a signal out of brake operation detecting means for detecting brake operation and the like; an automatic transmission for performing speed change control using as a hydraulic-pressure supply source a main pump driven by said engine; a solenoid valve for directly supplying from said main pump an engagement pressure of a forward engagement element of said automatic transmission; and a solenoid-valve control means for current-value controlling operation of the solenoid valve, wherein said solenoid-valve control means include means for outputting a command for at least more than a predetermined pressure required for complete engagement of said forward engagement element with regard to a current value of said solenoid valve when said idle-stop control means output a release command for releasing an idle stop of the engine after the idle stop.
The control system for an automatic transmission as described in claim 8 is provided with a solenoid valve for directly supplying from the main pump an engagement pressure of a forward engagement element of the automatic transmission and a solenoid-valve control means for current-value controlling operation of the solenoid valve.
And the solenoid-valve control means include means for outputting a command for at least more than a predetermined pressure required for complete engagement of the forward engagement element with regard to a current value of the solenoid valve when the idle-stop control means output a release command for releasing an idle stop of the engine after the idle stop.
Thus, there is no electric assist pump and the like in the prior art, so that when engine idle is stopped by the idle-stop control means, the electric assist pump is not continuously operated during idle stop as well.
Therefore, idle stop control can be performed without applying a load to the battery and the electric motor and at low cost.
Moreover, in the invention as described in claims 1 to 7, there is arranged no solenoid valve for each engagement element, requiring arrangement of the bypass circuit. On the other hand, in the invention as described in claim 8, there is arranged a solenoid valve for directly supplying the hydraulic pressure to the forward engagement element, so that by directly supplying oil to the hydraulic passages having oil discharged therefrom without waiting switching of the hydraulic passages by the shift valves, sufficient engagement pressure can quickly be supplied to the engagement elements.
With this, the forward engagement elements are engaged quickly to depress the accelerator pedal in the neutral state, preventing a problem of producing an engagement shock by engagement of the forward clutch with the engine at full throttle.
Finally, the invention as described in claim 9 provides the control system for an automatic transmission as described in claim 8, characterized in that said solenoid-valve control means include means for continuing said command for more than the predetermined pressure until a vehicle speed after vehicle restart becomes a predetermined value after a given time subsequent to restart of the starter motor or after the idle stop.
Therefore, in the control system for an automatic transmission as described in claim 9, the solenoid-valve control means include means for continuing said command for more than the predetermined pressure until a vehicle speed after vehicle restart becomes a predetermined value after a given time subsequent to restart of the starter motor or after the idle stop.
Specifically, since the discharge amount of the main pump is sufficiently obtained after a given time elapses after vehicle restart, or when the vehicle speed becomes a predetermined speed, hydraulic-pressure control can be performed as usual. However, at the initial stage of restart, sufficient discharge amount of the main pump cannot be obtained. In such a state, a current value of the solenoid valve is set at a value higher than that at normal control to secure the discharge amount required for engagement, obtaining smooth engagement of the forward engagement elements, allowing achievement of smooth running.